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feat(universal): spread() with fewer reactive nodes and a sources array; compilers emit it (#3424)

Port of @solidjs/web's spread (#3388, #3419) to the universal renderer:

- `ref` folds into the props effect and is re-applied only when its
  identity changes. `ref()` runs the callback untracked with no owner, so
  nothing a ref creates is disposed when the effect reruns.
- Children keep their own owned `insert` — that effect owns the child
  subtree, and merging it would rebuild the children on every prop change.
  A plain object whose `children` is a data property inserts the value with
  no effect at all. Three nodes become two with children through the
  spread, one without.
- A lone function source resolves inside each tracking scope; an ARRAY of
  sources is the union of their keys, later sources winning, only the
  winning source read, function sources called inline with no merge and no
  memo. Nullish sources are empty. Keys are still enumerated with for...in
  so a renderer's proxy props answer through their traps.

Both compilers' universal generate follows the dom generate: a lone spread
passes straight through (reactive included — the `mergeProps(() => expr)`
wrap that existed only because the runtime could not resolve a function is
gone), and several sources compile to the array instead of a mergeProps()
call. Universal has no hydration ids, so the runtime and compiler halves
land together.

Co-authored-by: Cursor <cursoragent@cursor.com>

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